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EP2128277A1 - Method for annealing metal strips - Google Patents

Method for annealing metal strips Download PDF

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Publication number
EP2128277A1
EP2128277A1 EP08164667A EP08164667A EP2128277A1 EP 2128277 A1 EP2128277 A1 EP 2128277A1 EP 08164667 A EP08164667 A EP 08164667A EP 08164667 A EP08164667 A EP 08164667A EP 2128277 A1 EP2128277 A1 EP 2128277A1
Authority
EP
European Patent Office
Prior art keywords
annealing
strip
caused
rolling
temperature
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP08164667A
Other languages
German (de)
French (fr)
Inventor
Mats Gartz
Ola Ritzen
Anders Carlsson
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Linde Sverige AB
Original Assignee
AGA AB
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by AGA AB filed Critical AGA AB
Publication of EP2128277A1 publication Critical patent/EP2128277A1/en
Withdrawn legal-status Critical Current

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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length

Definitions

  • the present invention relates to hot rolling of steel strips. More precisely, the invention relates to a method for annealing of steel strips in connection with such hot rolling.
  • strips of stainless steel are manufactured by rolling in for example Steckel type rolling mills, in which the strip is hot rolled in several steps between which steps the strip is coiled.
  • Another type of rolling mills is those of tandem type, in which hot rolling takes place at several parallel stations.
  • hot rolling takes place at a temperature of about 900°C - 1200°C, and is followed firstly by an annealing step at typically about 1100°C - 1200°C and thereafter by a pickling step.
  • the present invention solves the above described problems.
  • the invention relates to a method for use when hot rolling steel strips, where the strip in a first step is hot rolled, in a second step is annealed, and where it finally is coiled for storage, transport or additional processing, and is characterised in that the annealing is caused to be performed in an annealing furnace through which the strip is transported after the hot rolling but before the coiling.
  • Figure 1 is an overview over a method according to the present invention.
  • a strip made of steel, preferably stainless steel, 1 is hot rolled in a hot rolling step 2.
  • the hot rolling takes place in a rolling mill of Steckel type, but it may also take place in a rolling mill of tandem type.
  • the rolling temperature is conventional and typically lies between 900°C and 1200°C.
  • the strip 1 is transported, continuously and in the direction as indicated by the arrow 7, up to and through an annealing furnace 4, in which the strip 1 is annealed.
  • the annealing takes place at an essentially constant temperature of between 1100°C and 1200°C.
  • the strip 1 is further transported to a coiling station 5, where the strip 1 is coiled on a roll for storage, transport or additional processing, such as a cold rolling step.
  • annealing is caused to be carried out on the not yet coiled strip 1.
  • higher efficiency and better use of resources in the heating of the strip 1 to annealing temperature is achieved.
  • this heating is quicker than in case the coiled strip had been heated to annealing temperature. Only after annealing, the strip 1 is coiled at the coiling station 5.
  • the annealing furnace 4 is heated by at least one oxyfuel burner.
  • the oxyfuel burner is driven with a gaseous fuel, such as natural gas or propane, and an oxidant with an oxygen content of at least 80 percentages by weight.
  • the addition advantage is achieved that the heating efficiency increases further in comparison to annealing furnaces being heated by conventional air burners, and the heating is energy efficient even at the elevated temperatures at which annealing is performed.
  • the annealing furnace 4 is a tunnel furnace, and annealing of the strip 1 takes place continuously since the strip 1 is transported through the annealing furnace 4 with essentially constant velocity.
  • the strip 1 may be moving all the time, with no operation interruptions, until it has been coiled at the coiling station 5.
  • the strip 1 before annealing but after rolling, the strip 1 is caused to cool down from rolling temperature to a transformation temperature, at which precipitation and/or recrystallisation takes place in the material of the strip 1.
  • this transformation temperature is below about 400°C. This cooling down is performed in a conventional manner per se in a cooling down station 6.
  • cooling down may be performed only when necessary, depending on the material of the strip 1, desired final result, etc., however the cooling down function may be reconnected again when so is desired. In other words, an increased flexibility is achieved in the process, without adding any serious drawback as to its efficiency.
  • one or several DFI burners are used in a preheating step 3.
  • the DFI burners are driven with a gaseous fuel, such as propane or natural gas, and an oxidant with an oxygen content of at least 80 percentages by weight.
  • the strip 1 is heated so that it essentially reaches the desired annealing temperature before it leaves the preheating step 3. In this way, the strip 1 has the correct temperature even before it is brought into the annealing furnace 3, whereby annealing does not have to last longer than necessary.
  • the preheating step 3 is also arranged so that its power may be adapted to the temperature of the strip 1 at the entry into the preheating step 3.
  • this may be achieved by controlling the number of simultaneously switched on DFI burners, by controlling the power of the DFI burners, etc. In this way, a suitable preheating can be achieved, regardless of if a cooling down step is performed or not.
  • the annealing furnace 4 itself comprises one or several DFI burners, of the type described above, that in combination with one or several oxyfuel burners achieve the annealing of the strip 1.
  • a cheap, fast and efficient annealing of hot rolled steel strips is achieved, with no unnecessary thermal losses.
  • the annealing is not sensitive for neither the dimensions and the geometrical design of the preheated material, nor the distance between the heat source and the material, which is the case when using for example induction heating.
  • the extra processing step implied by having a separately arranged annealing furnace for coiled steel strips may be eliminated, which saves time as well as space, and which leads to increased production capacity, but also to diminished costs in terms of installation and maintenance.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Mechanical Engineering (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Heat Treatment Of Strip Materials And Filament Materials (AREA)

Abstract

Method for use when hot rolling steel strips (1), where the strip (1) in a first step is hot rolled, in a second step is annealed, and where it finally is coiled for storage, transport or additional processing.
The invention is characterised in that the annealing is caused to take place in an annealing furnace (4) through which the strip (1) is transported after the hot rolling but before the coiling.

Description

  • The present invention relates to hot rolling of steel strips. More precisely, the invention relates to a method for annealing of steel strips in connection with such hot rolling.
  • Today, strips of stainless steel are manufactured by rolling in for example Steckel type rolling mills, in which the strip is hot rolled in several steps between which steps the strip is coiled. Another type of rolling mills is those of tandem type, in which hot rolling takes place at several parallel stations. Typically, hot rolling takes place at a temperature of about 900°C - 1200°C, and is followed firstly by an annealing step at typically about 1100°C - 1200°C and thereafter by a pickling step.
  • Conventionally, strips have been let to cool down between hot rolling and annealing, and the strip has been reheated to the desired annealing temperature. This has resulted in an unnecessarily large energy consumption, as well as unnecessarily heavy material deterioration, among other things as a consequence of oxide scaling, and consequently leading to increased needs for cleaning and pickling.
  • In the article "Direktglühen - neue Strasse im Fertigungsverfahren von ferritischem, rostfreiem Stahl in Betrieb genommen", published in the journal GASWÄRME International (53) No. 7/2004, a method is disclosed in which the coiled steel strip is placed in an annealing furnace immediately following the last hot rolling step. Hereby, a large part of the thermal energy of the strip may be recovered for the annealing step.
  • However, it takes a non negligible period of time to heat such a steel strip coil from rolling temperature to annealing temperature, since heat conduction in the material is limited. Furthermore, during the heating process there are additional energy losses from which the material cannot benefit.
  • It is also possible to heat a rolled ccoiled strip by the use of induction heating. This is associated with smaller losses of energy. However, such heating is sensitive for the dimensions and geometry of the material, as well as for the distance between the heat source and the heated material, and plants for induction heating are also quite costly.
  • Moreover, in order for the handling of the coils between the rolling and the annealing not to unacceptably affect the rate of production, expensive logistics equipment is often required.
  • The present invention solves the above described problems.
  • Thus, the invention relates to a method for use when hot rolling steel strips, where the strip in a first step is hot rolled, in a second step is annealed, and where it finally is coiled for storage, transport or additional processing, and is characterised in that the annealing is caused to be performed in an annealing furnace through which the strip is transported after the hot rolling but before the coiling.
  • In the following, the invention will be described in detail, with reference to exemplifying embodiments of the invention and to the appended drawing, in which:
  • Figure 1 is an overview over a method according to the present invention.
  • A strip made of steel, preferably stainless steel, 1 is hot rolled in a hot rolling step 2. Preferably, the hot rolling takes place in a rolling mill of Steckel type, but it may also take place in a rolling mill of tandem type. The rolling temperature is conventional and typically lies between 900°C and 1200°C.
  • After the rolling, the strip 1 is transported, continuously and in the direction as indicated by the arrow 7, up to and through an annealing furnace 4, in which the strip 1 is annealed. According to a preferred embodiment, the annealing takes place at an essentially constant temperature of between 1100°C and 1200°C.
  • After annealing, the strip 1 is further transported to a coiling station 5, where the strip 1 is coiled on a roll for storage, transport or additional processing, such as a cold rolling step.
  • Thus, annealing is caused to be carried out on the not yet coiled strip 1. Hereby, higher efficiency and better use of resources in the heating of the strip 1 to annealing temperature is achieved. Furthermore, this heating is quicker than in case the coiled strip had been heated to annealing temperature. Only after annealing, the strip 1 is coiled at the coiling station 5.
  • According to a preferred embodiment, the annealing furnace 4 is heated by at least one oxyfuel burner. Preferably, the oxyfuel burner is driven with a gaseous fuel, such as natural gas or propane, and an oxidant with an oxygen content of at least 80 percentages by weight.
  • In case one or several such burners are used in an annealing furnace 4 of the type described herein, the addition advantage is achieved that the heating efficiency increases further in comparison to annealing furnaces being heated by conventional air burners, and the heating is energy efficient even at the elevated temperatures at which annealing is performed.
  • According to a preferred embodiment, the annealing furnace 4 is a tunnel furnace, and annealing of the strip 1 takes place continuously since the strip 1 is transported through the annealing furnace 4 with essentially constant velocity. Thus, the strip 1 may be moving all the time, with no operation interruptions, until it has been coiled at the coiling station 5.
  • According to a preferred embodiment, before annealing but after rolling, the strip 1 is caused to cool down from rolling temperature to a transformation temperature, at which precipitation and/or recrystallisation takes place in the material of the strip 1. According to a preferred embodiment, this transformation temperature is below about 400°C. This cooling down is performed in a conventional manner per se in a cooling down station 6.
  • According to a preferred embodiment, it is possible to temporarily refrain from the cooling down step by disconnecting the function of the cooling down station 6 from the process. In this way, cooling down may be performed only when necessary, depending on the material of the strip 1, desired final result, etc., however the cooling down function may be reconnected again when so is desired. In other words, an increased flexibility is achieved in the process, without adding any serious drawback as to its efficiency.
  • In order to quickly boost the temperature of the strip 1 before the annealing step and after the rolling step 2 or the cooling down step 6, according to a preferred embodiment one or several DFI burners are used in a preheating step 3. Preferably, the DFI burners are driven with a gaseous fuel, such as propane or natural gas, and an oxidant with an oxygen content of at least 80 percentages by weight.
  • According to a preferred embodiment, the strip 1 is heated so that it essentially reaches the desired annealing temperature before it leaves the preheating step 3. In this way, the strip 1 has the correct temperature even before it is brought into the annealing furnace 3, whereby annealing does not have to last longer than necessary.
  • In case a disconnectable cooling down step is used, according to the above said, according to a preferred embodiment the preheating step 3 is also arranged so that its power may be adapted to the temperature of the strip 1 at the entry into the preheating step 3. By way of example, this may be achieved by controlling the number of simultaneously switched on DFI burners, by controlling the power of the DFI burners, etc. In this way, a suitable preheating can be achieved, regardless of if a cooling down step is performed or not.
  • According to yet another preferred embodiment, the annealing furnace 4 itself comprises one or several DFI burners, of the type described above, that in combination with one or several oxyfuel burners achieve the annealing of the strip 1.
  • Hence, by using a method according to the present inventions, a cheap, fast and efficient annealing of hot rolled steel strips is achieved, with no unnecessary thermal losses. Moreover, the annealing is not sensitive for neither the dimensions and the geometrical design of the preheated material, nor the distance between the heat source and the material, which is the case when using for example induction heating.
  • Furthermore, the extra processing step implied by having a separately arranged annealing furnace for coiled steel strips may be eliminated, which saves time as well as space, and which leads to increased production capacity, but also to diminished costs in terms of installation and maintenance.
  • Above, preferred embodiments have been described. However, it is apparent for the skilled person that many modifications may be made to the described embodiments without departing from the spirit of the invention. Thus, the invention shall not be limited by the described embodiments, but may be varied within the frame of the enclosed claims.

Claims (10)

  1. Method for use when hot rolling steel strips (1), where the strip (1) in a first step is hot rolled, in a second step is annealed, and where it finally is coiled for storage, transport or additional processing, characterised in that the annealing is caused to take place in an annealing furnace (4) through which the strip (1) is transported after the hot rolling but before the coiling.
  2. Method according to claim 1, characterised in that the additional processing step is caused to be comprised of cold rolling.
  3. Method according to claim 1 or 2, characterised in that the strip (1) is caused to be cooled down to a temperature below the transformation temperature for recrystallisation and/or precipitation of the material before the annealing.
  4. Method according to any one of the preceding claims, characterised in that the annealing is caused to take place at an essentially constant temperature of between 1100°C and 1200°C.
  5. Method according to any one of the preceding claims, characterised in that the rolling is caused to be performed in a rolling mill of Steckel type.
  6. Method according to any one of the preceding claims, characterised in that the annealing furnace (4) is caused to be heated by at least one oxyfuel burner.
  7. Method according to any one of the preceding claims, characterised in that the strip (1) is caused to be preheated by at least one DFI burner.
  8. Method according to claim 7, characterised in that the strip (1) is caused to be preheated to the annealing temperature of the material.
  9. Method according to claim 7 or 8, characterised in that the DFI burner is caused to be arranged along the transportation path of the strip (1) between the rolling step and the annealing step.
  10. Method according to any one of the preceding claims, characterised in that the annealing furnace (4) is a tunnel furnace, and in that the annealing of the strip (1) is caused to be performed continuously by the strip (1) being transported through the annealing furnace (4) with a constant velocity.
EP08164667A 2008-05-29 2008-09-19 Method for annealing metal strips Withdrawn EP2128277A1 (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
SE0801262 2008-05-29

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EP2128277A1 true EP2128277A1 (en) 2009-12-02

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8709286B2 (en) 2008-10-30 2014-04-29 Archer Daniels Midland Company Reduction of HMF ethers with metal catalyst

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2630877B1 (en) * 1976-07-09 1977-11-24 Schloemann Siemag Ag Hot rolling of metal strip
US4861390A (en) * 1985-03-06 1989-08-29 Kawasaki Steel Corporation Method of manufacturing formable as-rolled thin steel sheets
EP0524162A2 (en) * 1991-07-17 1993-01-20 CENTRE DE RECHERCHES METALLURGIQUES CENTRUM VOOR RESEARCH IN DE METALLURGIE Association sans but lucratif Method of manufacturing a thin sheet of low carbon steel
WO1997046332A1 (en) * 1996-06-07 1997-12-11 Hoogovens Staal B.V. Method and apparatus for the manufacture of a steel strip
US5771732A (en) * 1995-04-19 1998-06-30 Sms Schloemann-Siemag Aktiengesellschaft Steckel mill
EP0937512A1 (en) * 1998-02-19 1999-08-25 Kvaerner Metals Continuous Casting Limited Low cost apparatus and method for manufacture of light gauge steel strip
EP1037721B1 (en) * 1997-12-08 2003-11-12 Corus Staal BV Process and device for producing a ferritically rolled steel strip

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2630877B1 (en) * 1976-07-09 1977-11-24 Schloemann Siemag Ag Hot rolling of metal strip
US4861390A (en) * 1985-03-06 1989-08-29 Kawasaki Steel Corporation Method of manufacturing formable as-rolled thin steel sheets
EP0524162A2 (en) * 1991-07-17 1993-01-20 CENTRE DE RECHERCHES METALLURGIQUES CENTRUM VOOR RESEARCH IN DE METALLURGIE Association sans but lucratif Method of manufacturing a thin sheet of low carbon steel
US5771732A (en) * 1995-04-19 1998-06-30 Sms Schloemann-Siemag Aktiengesellschaft Steckel mill
WO1997046332A1 (en) * 1996-06-07 1997-12-11 Hoogovens Staal B.V. Method and apparatus for the manufacture of a steel strip
EP1037721B1 (en) * 1997-12-08 2003-11-12 Corus Staal BV Process and device for producing a ferritically rolled steel strip
EP0937512A1 (en) * 1998-02-19 1999-08-25 Kvaerner Metals Continuous Casting Limited Low cost apparatus and method for manufacture of light gauge steel strip

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
ROHDE W: "COMPACT STRIP PRODUCTION (CSP): THE APPROACH FOR ECONOMICAL PRODUCTION OF HOT WIDE STRIP", CAHIERS D'INFORMATIONS TECHNIQUES DE LA REVUE DE METALLURGIE, REVUE DE METALLURGIE. PARIS, FR, vol. 91, no. 4, 1 April 1994 (1994-04-01), pages 529 - 540, XP000449405, ISSN: 0035-1563 *

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8709286B2 (en) 2008-10-30 2014-04-29 Archer Daniels Midland Company Reduction of HMF ethers with metal catalyst

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